Electronic device

ABSTRACT

An electronic device is provided. The electronic apparatus includes a controller and a dummy load. When the dummy load is turned on by the controller, the dummy load regulates a direct current (DC) output voltage outputted to the electronic device by a power conversion apparatus connected to the electronic device. Accordingly, the electronic device communicates with the power conversion apparatus using the dummy load to dynamically regulate the DC output voltage, so as to avoid power consumption.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefits of U.S. provisionalapplication Ser. No. 61/740,431, filed on Dec. 20, 2012. The entirety ofthe above-mentioned patent applications is hereby incorporated byreference herein and made a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates generally to a power control technique, and moreparticularly to a power supply system and an electronic device having apower saving function.

2. Description of Related Art

At present, due to the requirement for the reduced weight of consumers'electronic apparatuses (e.g., desktop computers, notebooks, mobilephones, digital cameras, tablet PCs, etc.), power may be supplied bybatteries within the electronic apparatuses or by means of externalpower adapters. That is, the electronic apparatuses require the powerconversion apparatuses (e.g., alternating-current (AC) to direct-current(DC) adapters) to supply power or to charge the internal batteries.

As to the existing power supply system, the power conversion apparatusis a passive equipment. Namely, when the input terminal of the powerconversion apparatus is connected to AC power, this power conversionapparatus passively provides the stable DC power to an electronicapparatus connected to the power conversion apparatus. However, once thepower conversion apparatus is connected to the AC power, the powerconversion apparatus may continue providing the DC power even though thepower conversion apparatus is not connected to any electronic apparatusor the electronic apparatus connected to the power conversion apparatusis in an off mode. Accordingly, the existing power conversion apparatusis unable to adjust the output power according to the state of theelectronic apparatus connected to the power conversion apparatus, whichleads to the significant amount of unnecessary power consumption.

SUMMARY OF THE INVENTION

The invention is directed to an electronic device capable of determiningthe state of the electronic device by the power value of the DC outputvoltage, and thereby dynamically regulate the voltage level of the DCoutput voltage, so as to effectively manage power consumption andachieve power savings.

In an embodiment of the invention, an electronic device is provided. Theelectronic device includes a controller and a first dummy load connectedto the controller. The controller turns on the first dummy loadaccording to a state of the electronic device. When the controller turnson the first dummy load, the first dummy load regulates a DC outputvoltage outputted to the electronic device by a power conversionapparatus connected to the electronic device.

According to an embodiment of the invention, the power conversionapparatus includes an AC to DC converter and a power conversion controlunit. The AC to DC converter is coupled to the electronic device, andthe AC to DC converter converts an AC input voltage to the DC outputvoltage according to a switch signal and provides the DC output voltageto the electronic device. The power conversion control unit is coupledto the AC to DC converter, and the power conversion control unit detectsthe DC output voltage to determine the state of the electronic device.When the electronic device is turned off, the power conversion controlunit sets the DC output voltage as a standby voltage through the switchsignal.

According to an embodiment of the invention, when the electronic deviceis turned on, the controller turns on the first dummy load, and thepower conversion control unit sets the DC output voltage as a normalvoltage through the switch signal, in which the normal voltage is higherthan the standby voltage.

According to an embodiment of the invention, the electronic devicefurther includes a second dummy load, in which the first dummy load andthe second dummy are used to regulate the DC output voltage.

According to an embodiment of the invention, when the electronic deviceis turned off, the controller turns on the first dummy load, and thepower conversion control unit sets the DC output voltage as the standbyvoltage through the switch signal. When the electronic device is turnedon, the controller turns on the second dummy load, and the powerconversion control unit sets the DC output voltage as a normal voltagethrough the switch signal, in which the normal voltage is higher thanthe standby voltage.

According to an embodiment of the invention, when the electronic deviceis cut off from the power conversion apparatus, the power conversioncontrol unit sets the DC output voltage as a ground voltage through theswitch signal.

According to an embodiment of the invention, the AC to DC converterincludes a converter circuit, a transformer, and a rectifier circuit.The converter circuit converts the AC input voltage into a first powervoltage according to the switch signal. The transformer converts thefirst power voltage into a second power voltage. The rectifier circuitconverts the second power voltage into the DC output voltage.

According to an embodiment of the invention, the power conversioncontrol unit includes a power detector, a counter, a feedback controlcircuit, and a pulse modulation controller. The power detector detectsthe power value of the DC output voltage. The counter counts apredetermined period when the power value of the DC output voltage iswithin a predetermined range. The voltage feedback circuit detects avoltage level of the DC output voltage, and the voltage feedback circuitoutputs a voltage setting signal according to the voltage level of theDC output voltage and a count result of the counter. The pulsemodulation controller outputs the switch signal according to the voltagesetting signal.

According to an embodiment of the invention, the pulse modulationcontroller includes a trigger circuit and a logic circuit. The triggercircuit outputs a switch trigger signal according to the voltage settingsignal. The logic circuit outputs the switch signal to the AC to DCconverter according to the switch trigger signal.

According to an embodiment of the invention, the power conversioncontrol unit further includes an optical coupling circuit transmittingthe voltage setting signal to the pulse modulation controller.

According to an embodiment of the invention, when the AC to DC converterreceives the AC input voltage, the power conversion control unitcontrols the AC to DC converter to output the DC output voltage having anormal voltage to the electronic device within a predetermined period,in which the normal voltage is higher than the standby voltage.

In view of the above, according to the embodiments of the invention, thepower supply system has the first dummy load configured in theelectronic device, such that the power value of the DC output voltage isadjusted according to the state of the electronic device. Therefore, thepower conversion control unit in the power conversion apparatus is ableto determine the state of the electronic device according to the powervalue of the DC output voltage. Moreover, the power conversion controlunit is able to dynamically regulate the voltage level of the DC outputvoltage according to the power requirement of the electronic device, andthereby save power by preventing unnecessary power consumption.

In order to make the aforementioned and other features and advantages ofthe invention comprehensible, embodiments accompanied with figures aredescribed in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of a power supply system according to anembodiment of the invention.

FIG. 1B is a driving waveform diagram of a power supply system accordingto an embodiment of the invention.

FIG. 1C is a schematic view of a pulse modulation controller accordingto an embodiment of the invention.

FIG. 2A is a block diagram of a power supply system according to anotherembodiment of the invention.

FIG. 2B is a driving waveform diagram of a power supply system accordingto another embodiment of the invention.

FIG. 3 is a flow diagram of a power control method of a power conversionapparatus according to an embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

In order to prevent unnecessary power consumption for a power supplysystem, embodiments of the invention provide an electronic devicesuitable for application in the power supply system. The electronicdevice in the power supply system is configured with at least one dummyload. Thereby, the electronic device may turn on the dummy load based ona state of the electronic device, and regulate a direct current (DC)output voltage outputted by a power conversion apparatus. The powerconversion apparatus may then obtain a power requirement of theconnected electronic device according to a power value of the DC outputvoltage, and thereby dynamically regulate a voltage level of the DCoutput voltage. Accordingly, the power conversion apparatus can providea suitable power source matching the requirement and achieve a powersaving effect.

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numbers areused in the drawings and the description to refer to the same or likeparts.

FIG. 1A is a block diagram of a power supply system according to anembodiment of the invention. With reference to FIG. 1A, a power supplysystem 100 includes an electronic device 110 and a power conversionapparatus 120. In the present embodiment, the electronic device 110includes a controller 111, a first dummy load 113, and a battery 115.The controller 111 may be an embedded controller or a keyboardcontroller, and the controller 111 may operate by receiving a DC outputvoltage Vdc provided by the power conversion apparatus 120 or byreceiving a power provided by the battery 115. The first dummy load 113may be implemented by physical circuit elements, such as in a circuitframework including resistors, capacitors, inductors, transistors,and/or combines thereof. The first dummy load 113 receives the DC outputvoltage Vdc, and the first dummy load 113 regulates a power value of theDC output voltage Vdc. The controller 111 may determine whether to turnon the first dummy load 113 according to a state of the electronicdevice 110. In other words, when the electronic device 110 is turnedoff, the power value of the DC output voltage Vdc is reduced. On theother hand, when the electronic device 110 is turned on, the controller111 may turn on the first dummy load 113, and therefore the power valueof the DC output voltage Vdc is increased. When the DC output voltageVdc reaches a predetermined value, the controller 111 turns off thefirst dummy load 113.

The power conversion apparatus 120 includes an AC to DC converter 121and a power conversion control unit 123. The AC to DC converter 121 iscoupled to the electronic device 110 and receives an AC input voltage ACand a switch signal Ssw. The AC to DC converter 121 converts the ACinput voltage AC to the DC output voltage Vdc according to the switchsignal Ssw and provides the DC output voltage Vdc to the electronicdevice 110. The power conversion control unit 123 is coupled to the ACto DC converter 121, and the power conversion control unit 123 detectsthe power value of the DC output voltage Vdc to determine the state ofthe electronic device 110.

When the electronic device 110 is turned off, such as in a state S5defined by Advanced Configuration and Power Interface (ACPI), the powerconversion control unit 123 may set the DC output voltage Vdc as astandby voltage through the switch signal Ssw, such as 5V, for example.When the electronic device 110 is turned on, such as in a state S0defined by ACPI, the power conversion control unit 123 may set the DCoutput voltage Vdc as a normal voltage through the switch signal Ssw,such as 19V, in which the normal voltage is typically higher than thestandby voltage.

The AC to DC converter 121 includes a converter circuit 131, atransformer TR, and a rectifier circuit 133. The converter circuit 131receives the AC input voltage AC, and the converter circuit 131 convertsthe AC input voltage AC to a first power voltage VP1 according to theswitch signal Ssw. The transformer TR converts the first power voltageVP1 to a second power voltage VP2. The rectifier circuit 133 convertsthe second power voltage VP2 to the DC output voltage Vdc. The rectifiercircuit 133 may be formed by a diode D1 and a capacitor C1, althoughembodiments of the invention are not limited thereto.

The power conversion control unit 123 includes a power detector 141, acounter 143, a voltage feedback circuit 145, an optical coupling circuit147, and a pulse modulation controller 149. The power detector 141detects the power value of the DC output voltage Vdc, in which the powerof the DC output voltage Vdc is related to the power of the second powervoltage VP2. Therefore, the present embodiment may determine the powervalue of the DC output voltage Vdc by detecting the power value of thesecond power voltage VP2, although embodiments of the invention are notlimited thereto. The counter 143 is controlled by the power detector 141to count for a predetermined period. For example, when the power valueof the DC output voltage Vdc is within a predetermined range, the powerdetector 141 controls the counter 143 to count for the predeterminedperiod.

The voltage feedback circuit 145 detects the voltage level of the DCoutput voltage Vdc, and the voltage feedback circuit 145 outputs avoltage setting signal Svs1 according to the voltage level of the DCoutput voltage Vdc and a count result CR1 of the counter 143. Theoptical coupling circuit 147 converts the voltage setting signal Svs1 toa voltage setting signal Svs2, and the optical coupling circuit 147transmits the voltage setting signal Svs2 to the pulse modulationcontroller 149. Moreover, the voltage setting signals Svs1 and Svs2 aresubstantially the same. However, the signal type of the voltage settingsignal Svs2 may be set according to a requirement of the pulsemodulation controller 149. For example, when the pulse modulationcontroller 149 is a current mode controller, then the voltage settingsignal Svs2 may be a current signal, although embodiments of theinvention are not limited thereto. The pulse modulation controller 149outputs the switch signal Ssw according to the voltage setting signalSvs2, so as to control the first power voltage VP1 outputted by theconverter circuit 131.

In one embodiment of the invention, the voltage feedback circuit 145 maybe further coupled to the power detector 141, such that the voltagefeedback circuit 145 outputs the voltage setting signal Svs1 accordingto the voltage level and the power value of the DC output voltage Vdcand the count result CR1 of the counter 143.

FIG. 1B is a driving waveform diagram of a power supply system accordingto an embodiment of the invention. With reference to FIGS. 1A and 1B,similar or same elements are labeled with similar or same referencenumerals. In a period T11, the AC to DC converter 121 receives the ACinput voltage AC and outputs the DC output voltage Vdc, and the powerconversion control unit 123 controls the AC to DC converter 121 tooutput the DC output voltage Vdc having a normal voltage Vnr. At thistime, the power detector 141 detects that a power value PW1 of the DCoutput voltage Vdc is within a predetermined range (between 0 to a powerdetection level LPD). Therefore, the power detector 141 controls thecounter 143 to count a predetermined time TD. Moreover, during thepredetermined time TD, the voltage level of the DC output voltage Vdc ismaintained at the normal voltage Vnr. The predetermined time TD may beset manually according to a circuit requirement, such as the responsespeed of the controller 111, although embodiments of the invention arenot limited thereto.

In a period T12, the counter 143 has counted the predetermined time TD.Therefore, the count result CR1 of the counter 143 is maintained, andthe power conversion control unit 123 controls the AC to DC converter121 to output the DC output voltage Vdc having a standby voltage Vst.Assume here that the electronic device 110 electrically connects to thepower conversion apparatus 120 at a time TA and provides the DC outputvoltage Vdc to the electronic device 110. However, assume that theelectronic device 110 is turned off at this time, which means that thefirst dummy load 113 has not been turned on. Here, the power value PW1of the DC output voltage Vdc is lower than the power detection levelLPD, and therefore the voltage level of the DC output voltage Vdc ismaintained at the standby voltage Vst.

In a period T13, assume that the electronic device 110 is turned on, andthe first dummy load 113 is turned on, such that the power value PW1 ofthe DC output voltage Vdc exceeds the power detection level LPD. At thistime, the power detector 141 controls the counter 143 to reset the countresult CR1, and the power conversion control unit 123 controls the AC toDC converter 121 to output the DC output voltage Vdc having the normalvoltage Vnr.

In a period T14, assume that the electronic device 110 is turned off,and the first dummy load 113 is not turned on. Therefore, the powervalue PW1 of the DC output voltage Vdc returns to be within thepredetermined range (between 0 to the power detection level LPD). Atthis time, the power detector 141 controls the counter 143 to count thepredetermined time TD. Moreover, during the predetermined time TD, thevoltage level of the DC output voltage Vdc is still maintained at thenormal voltage Vnr.

After the period T14, the counter 143 has counted the predetermined timeTD, and therefore the count result CR1 of the counter 143 is maintained.Moreover, the power conversion control unit 123 controls the AC to DCconverter 121 to output the DC output voltage Vdc having the standbyvoltage Vst. Since the electronic device 110 is turned off at this time,which means that the power value PW1 of the DC output voltage Vdc willnot exceed the power detection level LPD, the voltage level of the DCoutput voltage Vdc is maintained at the standby voltage Vst.

FIG. 1C is a schematic view of a pulse modulation controller accordingto an embodiment of the invention. With reference to FIGS. 1A and 1C, inthe present embodiment, a pulse modulation controller 149 a includes atrigger circuit 151 and a logic circuit 153, for example. The triggercircuit 151 outputs a switch trigger signal Strs according to thevoltage setting signal Svs2, and the logic circuit 153 generates theswitch signal Ssw according to the switch trigger signal Strs, and thelogic circuit 153 outputs the switch signal Ssw to the converter circuit131 of the AC to DC converter 120. The trigger circuit 151 may obtain anadjustment requirement of the DC output voltage Vdc according to thevoltage setting signal Svs2. Moreover, the trigger circuit 151 mayregulate the voltage level of the switch signal Ssw generated by thelogic circuit 153 through the switch trigger signal Strs, such that theAC to DC converter 120 correspondingly regulates the voltage level ofthe DC output voltage Vdc.

FIG. 2A is a block diagram of a power supply system according to anotherembodiment of the invention. With reference to FIGS. 1A and 2A, similaror same elements are labeled with similar or same reference numerals. Inthe present embodiment, a power supply system 200 includes an electronicdevice 210 and a power conversion apparatus 220. The electronic device210 includes a controller 211, a first dummy load 213, a second dummyload 215, and a battery 217. The functions of the battery 217 is similarto the battery 115. The first dummy load 213 and the second dummy load215 receive the DC output voltage Vdc to regulate the power value of theDC output voltage Vdc. The controller 211 may determine whether to turnon the first dummy load 213 and the second dummy load 215 according to astate of the electronic device 210. For example, when the electronicdevice 210 is turned off, the controller 211 may turn on the first load213, such that the power value of the DC output voltage Vdc isincreased. Thereafter, when the electronic device 110 is turned on, thecontroller 111 may turn on the first dummy load 213 and the second dummyload 215, and accordingly the power value of the DC output voltage Vdcis again increased.

The power conversion apparatus 220 includes the AC to DC converter 121and a power conversion control unit 221. The power conversion controlunit 221 includes a power detector 231, a counter 233, a voltagefeedback circuit 235, an optical coupling circuit 237, and a pulsemodulation controller 239. Since the functions and couplingrelationships of the power detector 231, the counter 233, the voltagefeedback circuit 235, the optical coupling circuit 237, and the pulsemodulation controller 239 are similar to the power detector 141, thecounter 143, the voltage feedback circuit 145, the optical couplingcircuit 147, and the pulse modulation controller 149, furtherelaboration thereof is omitted hereafter.

FIG. 2B is a driving waveform diagram of a power supply system accordingto another embodiment of the invention. With reference to FIGS. 2A and2B, similar or same elements are labeled with similar or same referencenumerals. In a period T21, the AC to DC converter 121 receives the ACinput voltage AC and outputs the DC output voltage Vdc, and the powerconversion control unit 123 controls the AC to DC converter 121 tooutput the DC output voltage Vdc having the normal voltage Vnr. At thistime, the power detector 231 detects the rise of a power value PW2 ofthe DC output voltage Vdc, and therefore the power detector 231 controlsthe counter 233 to count the predetermined time TD. Moreover, during thepredetermined time TD, the voltage level of the DC output voltage Vdc ismaintained at the normal voltage Vnr. Furthermore, assume that theelectronic device 210 is electrically connected to the power conversionapparatus 220 at a time TB to provide the DC output voltage Vdc to theelectronic device 210, such that the power value PW2 of the DC outputvoltage Vdc rises to be within a predetermined range (between the powerdetection level LPD and a system on level LSON) due to the first dummyload 213.

In a period T22, the counter 233 has counted the predetermined time TD,and the power value PW2 of the DC output voltage Vdc rises to be withinthe predetermined range (between the power detection level LPD and thesystem on level LSON). Therefore, the power detector 231 controls thecounter 233 to maintain a count result CR2. At this time, since thecount result CR2 remains fixed, this represents the electronic device210 is electrically connected to the power conversion apparatus 220 andthe electronic device 210 is turned off. Accordingly, the powerconversion control unit 221 controls the AC to DC converter 121 tooutput the DC output voltage Vdc having the standby voltage Vst.

In a period T23, assume that the electronic device 210 is turned on.That is, the first dummy load 213 is not turned on and the second dummyload 215 is turned on, such that the power value PW2 of the DC outputvoltage Vdc exceeds the system on level LSON. At this time, the powerdetector 231 controls the counter 233 to reset the count result CR2.Moreover, the power conversion control unit 221 controls the AC to DCconverter 121 to output the DC output voltage Vdc having the normalvoltage Vnr, and then the second dummy load 215 may be turned off

In a period T24, assume that the electronic device 210 is turned off,and the second dummy load 215 has not been turned on. Therefore, thepower value PW2 of the DC output voltage Vdc returns to thepredetermined range (between the power detection level LPD and a systemon level LSON). At this time, the power detector 231 controls thecounter 233 to count the predetermined time TD. During the predeterminedtime TD, the voltage level of the DC output voltage Vdc is stillmaintained at the normal voltage Vnr. Moreover, assume that theelectronic device 210 is cut off from the power conversion apparatus 220at a time TC. Accordingly, the power value PW2 of the DC output voltageVdc is reduced to be lower than the power detection level LPD.

After the period T24, the counter 233 has counted the predetermined timeTD. However, the power value PW2 of the DC output voltage Vdc hasreduced to be lower than the power detection level LPD. Therefore, thepower detector 231 controls the counter 233 to reset the count resultCR2, and the power conversion control unit 123 controls the AC to DCconverter 121 to output the DC output voltage Vdc having a groundvoltage (i.e. 0V).

Embodiments of the invention also provide a power control method of anelectronic device. By having the power conversion apparatuses 120 and220 obtain the power requirements of the connected electronic devices110 and 210 through the power value of the DC output voltage Vdc, asuitable power source can be provided and a power saving effect can beachieved.

FIG. 3 is a flow diagram of a power control method of a power conversionapparatus according to an embodiment of the invention. With reference toFIG. 3, in Step S302, the power conversion apparatus detects the powervalue of the DC output voltage, in which the power value of the DCoutput voltage corresponds with state of the electronic device. Indetail, the controller in the electronic device may turn on the dummyload according to the state of the electronic device, such that thepower value of the DC output voltage changes in accordance with state ofthe electronic device.

In Step S304, the power conversion apparatus determines whether theelectronic device is turned on. In specifics, the power detector in thepower conversion apparatus may determine the state of the electronicdevice by the power value of the DC output voltage.

In Step S306, when the electronic device is determined to be turned on,the power conversion apparatus provides the DC output voltage having thenormal voltage to the electronic device. In detail, when the powerdetector determines that the electronic device is turned on, the switchsignal provided to the AC to DC converter may be regulated, such thatthe AC to DC converter provides the DC output voltage having the normalvoltage to the power conversion apparatus.

In Step S308, when the electronic device is determined to be turned off,the power conversion apparatus provides the DC output voltage having thestandby voltage to the electronic device. In specifics, when the powerdetector determines that the electronic device is turned off, the switchsignal provided to the AC to DC converter may be regulated, such thatthe AC to DC converter provides the DC output voltage having the standbyvoltage to the power conversion apparatus.

Moreover, when the power conversion apparatus receives the AC inputvoltage, the AC input voltage may be converted into the DC outputvoltage having the normal voltage and provided to the electronic device.However, when the electronic device is still turned off during thepredetermined period, the power conversion apparatus provides the DCoutput voltage having the standby voltage to the electronic device.Furthermore, when the power conversion apparatus is cutoff from theelectronic device, the output of the DC output voltage may beterminated. That is, the DC output voltage having the ground voltage maybe outputted.

To sum up, according to the embodiments of the invention, the powersupply system has at least one dummy load configured in the electronicdevice, such that the power value of the DC output voltage is adjustedaccording to the state of the electronic device. Therefore, the powerconversion control unit in the power conversion apparatus may determinethe state of the electronic device according to the power value of theDC output voltage. Moreover, the power conversion control unit maydynamically regulate the voltage level of the DC output voltageaccording to the power requirement of the electronic device, and therebysave power by preventing unnecessary power consumption.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of theinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the invention covermodifications and variations of this invention provided they fall withinthe scope of the following claims and their equivalents.

What is claimed is:
 1. An electronic device, comprising: a controller;and a first dummy load connected to the controller, wherein thecontroller turns on the first dummy load according to a state of theelectronic device, wherein when the controller turns on the first dummyload, the first dummy load regulates a direct current (DC) outputvoltage outputted to the electronic device by a power conversionapparatus connected to the electronic device.
 2. The electronic deviceaccording to claim 1, wherein the power conversion apparatus comprises:an alternating current to direct current (AC to DC) converter coupled tothe electronic device, converting an AC input voltage to the DC outputvoltage according to a switch signal and providing the DC output voltageto the electronic device; and a power conversion control unit coupled tothe AC to DC converter, detecting the DC output voltage to determine thestate of the electronic device, wherein when the electronic device isturned off, the power conversion control unit sets the DC output voltageas a standby voltage through the switch signal.
 3. The electronic deviceaccording to claim 2, wherein when the electronic device is turned on,the controller turns on the first dummy load, and the power conversioncontrol unit sets the DC output voltage as a normal voltage through theswitch signal, wherein the normal voltage is higher than the standbyvoltage.
 4. The electronic device according to claim 2, wherein theelectronic device further comprises a second dummy load, the first dummyload and the second dummy being used for regulating the DC outputvoltage.
 5. The electronic device according to claim 4, wherein when theelectronic device is turned off, the controller turns on the first dummyload, and the power conversion control unit sets the DC output voltageas the standby voltage through the switch signal.
 6. The electronicdevice according to claim 5, wherein when the electronic device isturned on, the controller turns on the second dummy load, and the powerconversion control unit sets the DC output voltage as a normal voltagethrough the switch signal, wherein the normal voltage is higher than thestandby voltage.
 7. The electronic device according to claim 4, whereinwhen the electronic device is cut off from the power conversionapparatus, the power conversion control unit sets the DC output voltageas a ground voltage through the switch signal.
 8. The electronic deviceaccording to claim 2, wherein the AC to DC converter comprises: aconverter circuit converting the AC input voltage into a first powervoltage according to the switch signal; a transformer converting thefirst power voltage into a second power voltage; a rectifier circuitconverting the second power voltage into the DC output voltage.
 9. Theelectronic device according to claim 2, wherein the power conversioncontrol unit comprises: a power detector detecting the power value ofthe DC output voltage; a counter counting a predetermined period whenthe power value of the DC output voltage is within a predeterminedrange; a voltage feedback circuit detecting a voltage level of the DCoutput voltage, the voltage feedback circuit outputting a voltagesetting signal according to the voltage level of the DC output voltageand a count result of the counter; and a pulse modulation controlleroutputting the switch signal according to the voltage setting signal.10. The electronic device according to claim 9, wherein the pulsemodulation controller comprises: a trigger circuit outputting a switchtrigger signal according to the voltage setting signal; and a logiccircuit outputting the switch signal to the AC to DC converter accordingto the switch trigger signal.
 11. The electronic device according toclaim 9, wherein the power conversion control unit further comprises: anoptical coupling circuit transmitting the voltage setting signal to thepulse modulation controller.
 12. The electronic device according toclaim 2, wherein when the AC to DC converter receives the AC inputvoltage, the power conversion control unit controls the AC to DCconverter to output the DC output voltage having a normal voltage to theelectronic device within a predetermined period, wherein the normalvoltage is higher than the standby voltage.